[ovs-dev,v2] Documentation: add notes for TSO & i40e

When using TSO in OVS-DPDK with an i40e device, the following
patch is required for DPDK, which fixes an issue on the TSO path:
https://patches.dpdk.org/patch/64136/
Document this as a limitation until a DPDK release with the fix
included is supported by OVS.

Also, document best known methods for performance tuning when
testing TSO with the tool iperf.

Signed-off-by: Ciara Loftus <ciara.loftus@intel.com>
Acked-by: Flavio Leitner <fbl@sysclose.org>
---
v2:
- rebased to master
- changed patch links from net-next tree to patchwork
---
 Documentation/topics/userspace-tso.rst | 27 ++++++++++++++++++++++++++
 manpages.mk                            |  3 ---
 2 files changed, 27 insertions(+), 3 deletions(-)

Hi Ciara,

On Mon, Jan 20, 2020 at 09:28:13AM +0000, Ciara Loftus wrote:
> When using TSO in OVS-DPDK with an i40e device, the following
> patch is required for DPDK, which fixes an issue on the TSO path:
> https://patches.dpdk.org/patch/64136/
> Document this as a limitation until a DPDK release with the fix
> included is supported by OVS.
> 
> Also, document best known methods for performance tuning when
> testing TSO with the tool iperf.
> 
> Signed-off-by: Ciara Loftus <ciara.loftus@intel.com>
> Acked-by: Flavio Leitner <fbl@sysclose.org>
> ---
> v2:
> - rebased to master
> - changed patch links from net-next tree to patchwork
> ---
>  Documentation/topics/userspace-tso.rst | 27 ++++++++++++++++++++++++++
>  manpages.mk                            |  3 ---

The manpages.mk got included.

Also, now that the original patch is merged, maybe it would be
nice to include Fixes: <sha1> ("title") too.

fbl

>  2 files changed, 27 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/topics/userspace-tso.rst b/Documentation/topics/userspace-tso.rst
> index 893c64839..94eddc0b2 100644
> --- a/Documentation/topics/userspace-tso.rst
> +++ b/Documentation/topics/userspace-tso.rst
> @@ -96,3 +96,30 @@ datapath must support TSO or packets using that feature will be dropped
>  on ports without TSO support.  That also means guests using vhost-user
>  in client mode will receive TSO packet regardless of TSO being enabled
>  or disabled within the guest.
> +
> +When the NIC performing the segmentation is using the i40e DPDK PMD, a fix
> +must be included in the DPDK build, otherwise TSO will not work. The fix can
> +be found on `DPDK patchwork`__.
> +
> +__ https://patches.dpdk.org/patch/64136/
> +
> +This fix is expected to be included in the 19.11.1 release. When OVS migrates
> +to this DPDK release, this limitation can be removed.
> +
> +~~~~~~~~~~~~~~~~~~
> +Performance Tuning
> +~~~~~~~~~~~~~~~~~~
> +
> +iperf is often used to test TSO performance. Care needs to be taken when
> +configuring the environment in which the iperf server process is being run.
> +Since the iperf server uses the NIC's kernel driver, IRQs will be generated.
> +By default with some NICs eg. i40e, the IRQs will land on the same core as that
> +which is being used by the server process, provided the number of NIC queues is
> +greater or equal to that lcoreid. This causes contention between the iperf
> +server process and the IRQs. For optimal performance, it is suggested to pin
> +the IRQs to their own core. To change the affinity associated with a given IRQ
> +number, you can 'echo' the desired coremask to the file
> +/proc/irq/<number>/smp_affinity
> +For more on SMP affinity, refer to the `Linux kernel documentation`__.
> +
> +__ https://www.kernel.org/doc/Documentation/IRQ-affinity.txt
> diff --git a/manpages.mk b/manpages.mk
> index dc201484c..54a3a82ad 100644
> --- a/manpages.mk
> +++ b/manpages.mk
> @@ -104,7 +104,6 @@ utilities/bugtool/ovs-bugtool.8: \
>  utilities/bugtool/ovs-bugtool.8.in:
>  lib/ovs.tmac:
>  
> -
>  utilities/ovs-dpctl-top.8: \
>  	utilities/ovs-dpctl-top.8.in \
>  	lib/ovs.tmac
> @@ -155,8 +154,6 @@ lib/common-syn.man:
>  lib/common.man:
>  lib/ovs.tmac:
>  
> -lib/ovs.tmac:
> -
>  utilities/ovs-testcontroller.8: \
>  	utilities/ovs-testcontroller.8.in \
>  	lib/common.man \
> -- 
> 2.17.1
> 
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